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2 - Infection and Immunity > Transmission of Infection > Flashcards

Transmission of Infection Flashcards

1
Q

What is the chain of infection?

A

infectious agent > reservoir > portal of exit > means of transmission > portal of entry > susceptible host

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2
Q

What is virulence?

A

The ability of the microbe to cause disease

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3
Q

What is dose?

A

The number of microbes entering the body

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4
Q

What is the international unit for dose?

A

Infectious dose 50 (ID50)

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5
Q

Why are viruses grown on tissues?

A

they cannot grow in agar

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6
Q

What does a low id mean and what is ID?

A

low id = more infectious

id values compares infectivity of microbes across different species

ID50 is the amount of pathogen (dose) required to infect half of a sampled population

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7
Q

What two categories do virulence factors usually include?

A

exotoxins
endotoxins

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8
Q

What are examples of exotoxins?

A

P. gingivalis (protease)
S. aureus (enterotoxin & leukocidin)

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9
Q

What is an example of a endotoxin?

A

Lipopolysaccharide
(released by P. gingivalis & E. coli)

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10
Q

Where does e.coli usually infect?

A

urinary tract

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11
Q

Which reservoir do most pathogenic microbes that infect humans come from?

A

other humans

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12
Q

What are examples of different reservoirs for microbes?

A
  1. humans
  2. animals (anthrax)
  3. environmental (clostridium tetani spores in soil)
  4. fomites
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13
Q

What type of bacteria is clostridum tetani?

A

gram positive bacillus

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14
Q

When are microbes not easily recognised in patients?

A

when patients are health carriers (convalescent and asymptomatic)

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15
Q

What is the incubation period?

A

the time between contamination and the development of symptoms

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16
Q

What do long incubation periods mean?

A
  • longer time periods when the infecting microbe may be spread to others
  • greater spread of the disease because of more human contact
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17
Q

What is a asymptomatic carrier?

A

An infected person with no clinical evidence of disease, though signs and symptoms of the disease may have been evident earlier

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18
Q

What is a carrier?

A

(as well as their contacts) are usually not aware of their infectious state

19
Q

What is colonisation?

A

the presence of micro-organism (s) in or on a host, with growth and multiplication, but without any overt clinical expression (infection) at the time the micro-organism is isolated.

20
Q

What is an endogenous reservoir and why does it occur?

A

Caused by members of the normal flora if:
Flora becomes ecologically harmful due to population/gene expression shifts e.g. periodontal disease and dental caries

they become displaced to another body site or are allowed to invade deeper tissues (e.g. post-surgical infections)

21
Q

Is influenza endogenous or exogenous?

A

exogenous

22
Q

What did general dentists have raised antibodies to?

A

Flu A
Flu B
RSV

23
Q

What is the portal of exit?

A

Microbes must ESCAPE from the source to colonise a new host
* Mechanisms of escape vary depending upon the source.

24
Q

What can the mode of escape be?

A
  • NATURAL (e.g. coughing or sneezing)
  • ARTIFICIAL (e.g. blood donation or dental handpiece aerosols)
25
Q

What does COSHH classify human pathogens based on?

A

ability to cause infection (higher virulence)
severity of disease
vaccine and treatment availability
risk of population spread

26
Q

What is the Ro?

A

reproductive number
the number of cases one case generates on average
over the course of its infectious period.

27
Q

Ro < 1 VS Ro > 1

A

When Ro< 1 infection will die out in the long run

When Ro>1 infection will be able to spread in a population

28
Q

What factors affect the Ro?

A

Ÿ Duration of infectivity
Ÿ Infectiousness
Ÿ Number of susceptible people

29
Q

How do respiratory viruses exit?

A

Droplets & aerosols Respiratory secretions

30
Q

Airborne vs Droplet

precautions

A

Airborne precautions = less than 5 microns, tiny particles, travel further and remain in air longer (respiratory precautions)

Droplet precautions = more than 5 microns, large particles (non respiratory precautions)

31
Q

What respiratory infections are accepted to be mostly transmitted by the airborne (aerosol route)?

A

a. tuberculosis,
b. measles
c. chickenpox

32
Q

If the particle is larger, will it fall slower or faster than smaller?

A

larger = slower

33
Q

What is an aerosol?

A

An aerosol is a suspension of fine solid particles or liquid droplets in air or another gas

34
Q

What does survival depend on?

A

persistence, stability, retention of infectivity

35
Q

What is fomite mediated transmission dependant on?

A

Environmental factors

Time between reservoirs

Efficiency of transfer

Dose of virus

36
Q

Why is fomite transmission difficult to prove?

A

respiratory transmission from asymptomatic people cannot be ruled out

37
Q

What is a barrier to fomite transmission?

A

hand hygiene

38
Q

How can aerosols be mitigated in dentistry?

A

-Use of rubber dam
-High/low volume aspiration
-Surgery ventilation

39
Q

How many air changes per hour?

A

10

40
Q

Where are the portals of entry?

A

*Respiratory tract (influenza)
*Gastro-intestinal tract (norovirus)
*Open/surgical wounds (staph. aureus)
*Medical devices/Sharps injuries (Hep b)
*Sexual contact (HIV)

41
Q

How can influenza virus enter?

A

*Respiration (aerosols)
*Inhalation (all particles)
*Direct contact (droplets)
*In-direct contact (settled particles – face touching)
* Role of conjunctiva uncertain

42
Q

What is a susceptible host?

A

Is a person who is at risk of infection as they are unable to fight the infection due to;

*An underdeveloped immune system (neonate)
*A declining immune system (elderly)
* Disease or drugs that impair host defences
*Breaks in the skin
*Medical devices

43
Q

What are the risk groups?

A

Elderly, young children, pregancy & chronic medical conditions (diabetes, asthma, heart disease)

2 - Infection and Immunity (12 decks)

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